That Time the Straw Hat Pirates Docked at Hogwarts
by Kariz
Summary: The Straw Hat Pirates find themselves sent off track from their adventure, and end up in an entirely unfamiliar world. But what else is new? Hogwarts, on the other hand, are struggling to keep up with the excitement. AU – Crossover.


There are spoilers for One Piece, up to chapter 513 I guess (to be safe) and 'Harry Potter and the Deathly Hallows' (so basically, recommended for people who've already finished reading HP)

This is an AU which takes place at some point in Harry's last year of Hogwarts, after 'Deathly Hallows'. As for the Straw-hats, think of this as after the time skip, but before they set off to Fisherman's Island. Imagine that they were sent away again by Kuma's powers. It doesn't sound very realistic, but it's an AU :P

I'm predicting this to end up with around 3 chapters. I find it hard to keep characters IN-character, so please tell me if you see any gaping plot holes or if you think some of the stuff the characters do or say are weird. Criticism is good, as long as it's not mean and actually useful!

Disclaimer: I don't own Harry Potter or One Piece :(

**The Straw Hat Pirates find themselves sent off track from their adventure, and end up in an entirely unfamiliar world. But what else is new? Hogwarts, on the other hand, are struggling to keep up with the excitement. AU – Crossover.**

**(xxx)**

Harry will never forget the day a ship rose out of the waters of the lake. A pirate ship. Hogwarts had received a guest, unannounced. Everyone stared with confusion as the enormous ship buoyed cheerfully on top of the murky waters. The ship's flag waved happily in the breeze. It took Harry a bit too long to realize that the paint on it depicted a grinning skull and crossbones with... a straw hat?

As soon as the stranger standing on deck spotted the people who were gathering by the lake to get a closer look, he gripped the rail of the ship with his two arms, pulled himself back until he was stretching his arms _impossibly_ far, and then jumped and flew with the momentum. People around Harry screamed in shock. The man landed in front of them accurately and with no fear, hopping a few times to catch his balance. He had just flown through the distance of half the lake without a broomstick, and yet his smile was impossibly wide as he introduced himself. Harry mentally corrected himself, _boy - not man. _That was the day everyone first saw Luffy-the-future-pirate-king. He was sure cheerful for someone who was lost. Everything about him was very bright - especially his smile and his clothes; a sleeveless red top adorned with sunshine buttons, denim blue shorts, a yellow sash holding it up, and a straw hat - which happened to look very similar to the one on the flag.

By the time Professor McGonagall and the rest of the teachers had arrived at the scene, something else happened. The air suddenly seemed to charge up in a split second. The air was heavy, and for those few seconds, Harry found it difficult to breathe. Then all of a sudden it stopped. Harry quickly glanced around him but all he got was a questioning look from Ron. No one else seemed to have felt that. The only way Harry could describe it was, that it popped, like a balloon or a bubble. After the air popped, someone called out from the ship.

It was a very beautiful and tall, mature-looking woman. She was someone with dark hair, dark eyes and a characteristic nose; someone who was almost too attractive. The future-pirate-king had called out with surprise "Ah! Robin!" and then proceeded to yell "_where was everyone else_?".

The woman stepped up onto the edge of the ship elegantly, and then _wings sprouted from her back_. She took a step off the ship and then flew down to the bank, several more students screamed in shock and jumped back. As soon as she reached a safe distance from the ground, the woman's wings disappeared and she stepped down lightly onto the ground (in heels, no less!). Maybe it was the way the sun reflected off the wings, but Harry swore that those wings of hers weren't made of feathers. No - they were made of _hands_. But, perhaps he saw wrong.

The rest of the teachers tried to follow McGonagall and the strangers back to her office, but she quickly pulled the teachers aside and muttered something. It looked like she had to spend a couple extra minutes to argue with Professor Foley, the new Defense Against the Dark Arts teacher - who took his job very seriously, before he finally nodded and stepped back with a worried look. The man with the straw hat and the dark haired woman were lead back to McGonagall's office.

Harry and the rest so desperately wanted to follow them. They decided to meet Harry back in the common room later on because they couldn't all fit under the invisibility cloak. He slipped away from the crowd to quickly don his invisibility cloak. He managed to catch up with the two strangers and Professor McGonagall. The headmistress stepped into her office and held the door open for the two strangers.

The boy mindlessly walked in, and Harry was about to take advantage of the opportunity he saw, where the woman had paused for a moment, just enough to let Harry slip in before her, but then the woman spoke. She turned and faced Harry directly, not quite meeting his eyes, but staring through the spot he was in. As if she knew he was there, but couldn't quite see him.

"I have met invisible strangers before."

Harry did his best, but he couldn't help but breathe in sharply with surprise. And a bit of fear. ("What did you say, Robin? That was kinda random, huh.") Her eyes were heavy with reproach, and Harry felt a little bit like he was being scolded by a motherly figure, such as Mrs Weasley.

"I will offer you a choice. Either you expose yourself now, or leave us."

Harry fled.

When he was finally in the common room, shivering in a cozy corner with his two best friends sitting by his sides, worried, he couldn't quite explain the cold sweat that dampened his skin. It wasn't as if he had tired himself out from running, but as if he was still shivering from the memory of the _look _he was given.

"I can't quite explain it… it was like Mad-eye Moody staring through you. Like, she knew I was there but she was just waiting - waiting for me to… I don't know."

"She wasn't even fazed that there was someone invisible in her presence? Not to forget, that she also offered you a choice of escaping without revealing yourself..."

"Merlin, that's scary! How she just let you off like that… that's down right suspicious."

Harry grimaced. "Maybe she was just confident that she could take care of things if she needed to, no matter what type of person she was facing."

They were silent after that, considering the woman and her cheerful companion.

**(xxx)**

Professor McGonagall stopped Harry on the way to lunch.

"Mr Potter, was that you in the office earlier?" She asked sternly.

"Erm. Sorry Professor… we just - I just wanted to know who they were."

She sighed and rubbed the bridge of her nose between her finger and thumb. "Mr Potter, do you not realize how dangerous that situation could have been? They were unknown people. We didn't even know what their intentions were."

Harry frowned. "But then why did you talk to them by yourself? What if they attacked you? You should've had other teachers with you!"

To his surprise, the woman's stern face relaxed into a soft smile. "Thank you for your concerns. But I assure you, I had the security in that office upgraded. There would've been no great catastrophe should things have gone wrong."

Harry's face warmed up with embarrassment. "Erm. Well… so… did you find out what they wanted?"

Professor McGonagall let out a weary sigh, which combined with her softened expression made Harry uncomfortably aware just how old she was. "Of course I am not in a position to tell you, but I suppose you would break even more rules to find out, you and your horribly curious friends.

"They are pirates, and from the very confusing conversation we had earlier, they are from a very different part of the world. I am tempted to say that they may even be from a different world altogether, because we had no mutual knowledge of the land and sea. But that is impossible. They are not familiar with witches and wizards, yet they have extraordinary powers that muggles would not be able to imitate. They were interrupted in their glorious journey for a famous treasure, and were ultimately 'vanished' by an enemy. The conclusion Miss Robin came to was that they were all sent here, Hogwarts, but for some reason are arriving at different times. At the moment, I have offered them Hogwarts as a temporary shelter whilst they wait for the rest of their crew to arrive."

She said all this with an impassive tone, almost reciting all this from her memory. She smiled at him ruefully after asking him "Is that all, Mr Potter?"

Harry blinked. That was easier than expected. He thanked her before rushing off to tell Ron and Hermione in a hushed tone in a hidden corner.

**(xxx)**

"I wonder how they got here." Hermione said during dinner that night.

"That ship of theirs is unusually large for a ship." said Ron.

They puzzled about that for a moment.

"What do you mean? I think that's a pretty reasonable size for a ship." Hermione replied.

"What? That ship is huge!"

"I guess that makes sense. Think about wizard tents, Hermione." Harry said, chewing around his potatoes.

At that moment, the two strangers walked into the hall. The chattering made by the students fell to a hush as one by one, people noticed who had just walked in.

Harry, and everyone else, watched the boy with the hat yell with shock about how much food there was, and watched how the woman almost laughed with amusement as the boy rushed to the nearest table (which happened to be Ravenclaw) and immediately started eating, alternating stuffing his face with one hand and grabbing more food with the other. The woman walked calmly at her own pace, following the boy.

They sat down in an empty spot by the end of the Ravenclaw table near the Hall doors. The stares from people around them didn't seem to have an effect whatsoever. At some point, the students sitting next to them had pulled out the courage to ask them questions. It became a regular occurrence. The two pirates would join the students in the Great Hall during mealtimes. By the end of the week, the information students had managed to discover had spread like fire.

The boy declared himself as "Luffy-the-Pirate-King" and was easily excitable. They soon found out he was twenty one years old ("_TWENTY-ONE? But he acts as if he's ten!")_. The only thing he was interested in was food, and 'One Piece' (which no one could explain what it was). He spent the following days disappearing from the castle and often managed to come back right on time for breakfast and dinner. One time, during a Quidditch practice, Harry glanced up for no reason and could have sworn he saw the boy swinging from the roofs of the castle. Strangely enough, he was the captain of the ship. It was strange enough imagining this woman following orders from someone so childish, but even more strange to imagine that he had a whole ship full of people who followed him.

The woman called herself Nico Robin, and asked others to call her Robin. She was interested in history and was often seen browsing through the books from the History section of the library, walking around the corridors of the castle. A few times people said they saw her stop in the middle of a corridor and strike up a conversation with a portrait or two.

They were both apparently very kind, and Harry couldn't help but be confused at how these two people didn't match up with his expectations of what a pirate should be. Where was the eye patch? Where was the wooden leg and the crude manners? Why was there a woman in the crew? They were strange pirates.

The Golden trio wondered about the rest of the crew. How long would they have to wait for the rest to arrive? Surely a pirate crew would have a lot of members. Hermione asked aloud if it was a good idea to let a large number of pirates to roam Hogwarts. Harry didn't know.

**(xxx)**

"Do you think he's her son?" wondered Ron during dinner a week later.

Harry spared a moment to feel nervous; he was watching the woman, who was chewing her food thoughtfully when she suddenly let out a laugh. Harry was nervous because he had never seen her laugh in her entire stay at Hogwarts, and the laugh had been so well timed, as if she had heard Ron's question. Harry became even more anxious when she immediately stopped herself, as if trying to pretend she hadn't heard, and then she glanced up and looked past all the students sitting in between them _and she looked at Harry in the eye._

Hermione hummed in agreement "That makes sense. But she's awfully young!"

The woman smiled before breaking their eye contact and returning to her food. Harry waited until they were back in the common room before telling his friends what he thought might've happened.

"I'm gonna follow her tomorrow. It's the weekend so we have no classes. I want to know what she does in her spare time."

Hermione argued that he shouldn't, Ron thought he should do it but take them along with him, and in the end they finally agreed that Harry could go investigate if they were allowed to follow him from far away with the Marauder's Map.

As they left to go to bed, Neville walked past.

"Oh, Harry-" Neville frowned and stared at Harry's shoulder as Harry turned around, confused.

"What's the matter, Neville?"

"Oh." the boy blinked and rubbed his eyes, "I must be getting tired. Sorry, I thought I saw something on the back of your cloak!"

Harry frowned and took his cloak off to inspect it whilst Neville chuckled to himself.

"I even thought it was an ear!"

**(xxx)**

The next day, Harry followed the woman like he said he would. He mostly did it without his invisibility cloak as during the day the corridors were more crowded. It would've been more difficult to follow the woman without bumping into people. However, she stayed in the library the entire time, even missing lunch to finish reading a book by the window.

Just as it began to turn dark and people began filtering out to head for dinner, the woman finally moved. She got up to put a book away, and Harry followed her actions to see if he would have to get up and follow her. If she left the library, he decided he would put on his invisibility cloak now and then follow her.

To his surprise (and a little bit of fear), the woman put her book away and then walked over straight to where Harry sat. She sat down opposite him and stuck an elegant hand out.

"Hello, my name is Nico Robin. But, please, just call me Robin."

Harry hesitantly took her hand. "Hi. I'm Harry Potter."

He was used to people's reactions. Very often than not, people would stare at his eyes and then stare at his forehead, trying to see the rest of the scar as they realize part of it was peeking out from behind his hair. Sometimes he met some very polite people who tried their best to conceal their shock and just let their eyes linger for a few seconds too long on his forehead, before moving on.

So when Nico Robin didn't even bat an eyelash at his name and shook his hand as if they were truly strangers, as if she didn't know his life story from reading the newspaper every day, who could blame him for feeling shocked? Somewhere in his mind, something flickered, and he couldn't help but remember what Professor McGonagall had said.

_They may even be from a different world altogether._

"You could hear us from across the hall."

She didn't reply. Instead, she sat back in her chair and tilted her head, as if asking him to elaborate.

"I mean… last night at dinner. My friend asked if you were the mother of… erm, the captain. You heard that, didn't you?"

"How do you turn invisible?"

Harry grimaced. How did she know? Everything was so confusing. Instead of finding answers, Harry felt like he was creating more and more questions for himself.

"I understand that you don't quite trust us because you don't understand us. That's fine. Not many people understand us. I would like to assure you that we have no plans to damage this place. We are only waiting for our comrades. As soon as everyone arrives, we will depart."

Harry wanted to ask more questions. But he couldn't quite wrap his mind around the situation fast enough.

Suddenly, the air pressure increased. He opened his mouth in surprise at the familiar feeling of the air becoming denser – and then suddenly releasing all the pressure with a _pop. _He frowned when the woman across him didn't react, but continued to watch him with a little bit of confusion.

"Erm. I think that thing just happened again. I think one of your friends arrived."

For once, she looked very confused and wasn't in control of everything. "How do you know?"

"Didn't you feel that? The air pressure? Everything just… popped."

She gave him a look that told him she didn't feel it, but she smiled. "Well then. I should go welcome whoever has arrived."

The woman stood up and left, Harry close on her heel. As they reached the Entrance Hall, Harry was hit with the strange realization that she had navigated the corridors and moving stair cases with ease and yet, she had only been here for a week.

He put his thoughts away for later as they approached the lake, where the large ship ("It's called the Thousand Sunny! That's what Luffy said to Padma, apparently!") was moored. Sure enough, a man with green hair and a green cloak was standing on deck. A second later, the air pressure increased again and Harry held his breath.

Another woman appeared. A few minutes passed where the two newcomers seemed to be slightly dazed, and then the man gazed at their surroundings before gesturing to Robin. The other woman quickly ran over to the side of the boat to stare, then turned back to the man. They seemed to be yelling about something, but Harry couldn't quite hear them from the distance.

From next to him, Robin breathed a sigh. He understood she had sighed with relief after she spoke, "It's good to know that the rest are actually arriving."

The woman and the man on board disappeared for a few minutes before re-emerging in a smaller boat, similar to the size of the boats the first years travel in before the sorting ceremony. As the boat came closer, Harry couldn't help but flush with embarrassment. The woman and the man both wore very exposing clothes. The woman had long, auburn curls, and she wore a very revealing bikini top with low slung jeans. Her outfit was very provocative, and to top it off, she wore a pair of high heeled sandals.

The man on the other hand wore what seemed like a green cloak at first, but it was loose in the front to the point that it exposed almost his entire chest. Harry couldn't help but stare at the disturbing scar that ran diagonally across his chest, the ends of it not even visible despite how much skin was already showing.

As the two people stepped onto land, the woman launched herself at Robin, hugging her with happiness.

"Robin! Thank goodness you're here!"

Harry noticed that the auburn-haired woman had a striking tattoo swirled over her shoulder, the black contrasted intensely with her pale skin.

"Who's this?" The man said; his voice deep and his face set in an almost bored expression. He was looking at Harry, not quite meeting his eye as an equal but more like watching a stray animal and wondering if they were going to cause any unnecessary trouble at all. He had his left eye constantly closed, the scar running vertically through his eyelid explained why.

The air popped again.

He looked back towards the ship. They were popping out like nobody's business! Harry was intimidated by the green-haired man, and he wondered again if it was a good idea that there were going to be so many pirates here at Hogwarts, especially if they were like this man in front of him. Even though he only had one eye to glare with, one eye was all he needed.

But the second man to arrive turned out not as frightening. He had shouted with confusion and relief once spotting the group. He was very muscular, but the fact that he was capable of displaying emotions unlike the green-haired man and Robin was a relief. Harry slipped away and left the group; the second man joined the rest by swimming over, and Harry let them reunite in peace (actually Harry had just noticed that the green-haired man had _three_ swords hanging by his side… no normal person wouldn't be slightly intimidated at the thought of being interrogated by this man!)

**(xxx)**

Later on, Harry learnt that they were Nami, Zoro and Usopp. He also soon figured out that having women, regardless of age, aboard a pirate ship was clearly not a problem.

Even though Nami was very pretty and very sexy, she didn't take crap from anyone. Lee Jordan had tried to flirt with her, and ended up being used so that the woman could find out more about the kitchens and why food appeared almost magically (not that Lee minded). A Slytherin tried to offer her with a proposition, and was promptly knocked out. The Slytherin later woke up in an empty classroom with several new bruises and his face drawn all over with a black marker. Harry later heard in passing that the captain, Luffy, and the man with the long nose, Usopp, were the ones who drew on the Slytherin's face.

One time, an angry student had yelled at Nami for being a tease. He cursed at her and called her a slut. He accused her of being tossed around like a prostitute, doing anything for money, and that she probably enjoyed all that. This happened when she was on a walk with the captain, Luffy. Shockingly, the normally mischievous and unapologetic woman had apparently froze with what people said was sadness. But Harry imagined the scene in his head and could only picture her freezing with anger. Later, Neville, one of the few witnesses, confirmed that Harry was more accurate than the gossip-version that the Hufflepuff girls were spreading, except that he might've seen maybe just a little bit of hurt in the shine of her eyes.

Funnily enough, Luffy did not react very kindly to the insults the student had spouted. The captain himself had apparently knocked the boy out with one powerful punch, something no one really believed because, well, the captain? Angry? That was impossible! Luffy was always smiling and laughing. Most people dismissed these rumours.

It was weird, but Harry accepted that the captain of this pirate crew was childish and enjoyed silly things. He accepted that this childish captain lead a crew of people, some who had obviously experienced great dangers before.

When he mentioned how strange this was, Hermione voiced her opinion.

"I think the question isn't how such a young, mindlessly happy boy can be the captain of these possibly dangerous people, but why do such people follow his orders without a doubt in their mind?"

**(xxx)**

The trio had been part of a very friendly conversation with Usopp along with Neville and several other Gryffindors one day. Usopp had sat in their midst during one lunch, and he had proceeded to tell his stories with barely a prompt from the students. The stories he had told were amazingly wild and most of the Gryffindors who heard them had snorted at such absurd tales.

But at some point they had moved along to talking about the Thousand Sunny, and every one of them could sense the love behind the man's words for the ship. They had recognized that there were at least a grain of truth behind each story, and Usopp and the Straw Hat pirates had probably travelled through dangerous times with their ship.

The next morning, Harry woke up to the feeling of the air popping again. Usopp had told his audience that there were thousands of people part of their crew, but when it was obvious most of them were doubtful and a few refused to believe him, he admitted grudgingly that there were only nine people in their crew at the moment ("But Luffy eats enough for hundreds!" and no one doubted that). The number was so shockingly small, people almost doubted him again (but, if there is anything anyone has learnt about Usopp, it's that he over-exaggerates rather than under).

_'Only three left' _thought Harry.

Harry and the others went down to breakfast quite early that day. It was so early that the Straw Hats were nowhere to be seen yet. As more and more students began to file in, Harry and the others overheard a bunch of girls gabbing.

"Did you hear? Apparently Neville was talking to that guy with the long nose. That man kept telling Neville weird stories - and apparently he said that their boat was part of their crew… Isn't that creepy? They must all be delusional if they think a _boat_ is part of their 'family'!"

Usopp may have been overachieving with his stories, but more importantly, you could tell that he was a harmless man who genuinely cared about his friends. Which was Harry and Ron were quick to send retorts flying at the gaggle of silly girls.

"It's not a boat, it's a ship!" Harry snapped at the gossiping girls.

Ron joined in almost as quickly "and those stories aren't weird! They're amazing! Who has the imagination to tell stories of sea kings and giant goldfishes that eat islands!"

The girls fled before they could say more.

"Actually," said Hermione, "if you think about it, it makes sense that their ship is so important to them. In the sea, far away from their homeland, where the weather and water can be so unpredictable, a pirate's ship is their only haven - the only home they can rely on. It's the very vehicle that brings them away from danger and to their dreams and adventure, isn't it? It's quite a romantic idea."

"Hermione, you're not thinking of becoming a pirate are you?" Ron grinned at her cheekily. "You're practically in love with the idea already."

"Of course not! Besides, there aren't libraries in ships - what would I do with my life if I couldn't even read books."

Harry frowned. "But, Hermione… You could just as easily bring that bottomless purse of yours and store a library in there. That's a terrible excuse."

An unfamiliar, yet very familiar, voice suddenly joined in from in front of them. "Actually, we do have a library on board the Thousand Sunny." It was the pretty navigator. She introduced herself as if she didn't know the whole school had been spreading any facts and information they could grasp onto about the strange pirate crew. "I'm Nami, navigator for the Straw Hat Pirates" She grinned.

Before they could reply, she piped up again. "I know who you all are. And I was wondering if you could tell me how you made this." She held up the Marauder's Map.

"How did you-?"

"That's Harry's!"

"What did you mean there's a library on your ship?"

She quickly pulled it away from their reaching grasps, leaning back casually away from their reaching hands.

"Tell me how you made it. And then maybe I'll give it back." she winked at them.

"But… how did you even get it? It was in my bag the whole time!"

Out of nowhere, the green haired swordsman plopped himself down next to the auburn-haired navigator, an animal with antlers and a pink hat sitting on his shoulders. "That's because she's a no-good thief." he rolled his eyes at her as she stuck her tongue back childishly. The little animal clambered down from the man's shoulders and sat in between the two humans.

"Oh! Chopper! When did you get here?"

"Just now- Uwah! So much food!"

Ron choked. "WHAT! A TALKING MOOSE?"

"SHUT UP! I'M A REINDEER NOT A MOOSE!"

**(xxx)**

**(A/N):** I like to imagine that Robin wakes up super early to explore the castle! She probably likes Hogwarts quite a bit 'cause it has so much history in it :P I didn't want this to be that long. Some scenes just started stretching out longer than I expected, and some just flew by exactly as I wanted. If there are any questions please ask me! I think that would help me improve this. Again, incorrect spelling or bad grammar or anything, tell me because I don't have someone to proof read it for me. It's all you guys :D

Update: Someone caught me out! Thanks Rachel, for catching my mistake!


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